Towards early dark energy and $n_s$=1 with Planck, ACT and SPT

TL;DR

This study explores how combining recent CMB data suggests non-zero early dark energy fractions and supports a scale-invariant primordial spectrum, potentially resolving the Hubble tension.

Contribution

It provides new constraints on early dark energy models using combined CMB datasets and discusses implications for the Hubble tension and primordial spectrum.

Findings

Combined CMB data favor non-zero EDE fractions.

Axion-like EDE fits data better than ΛCDM, especially with ACT data.

Results support a scale-invariant spectrum if local H0 measurements are correct.

Abstract

We investigate the constraints on early dark energy (EDE) by combining the most recent CMB observations available, ACT DR4, SPT-3G, and Planck2018 ($\ell_\text{TT,max}=1000$) data. This combined CMB dataset favors non-zero EDE fractions and large Hubble constants. The inclusion of BAO+Pantheon data has little effect on the results, leads to $H_0=71.6( 72.9)_{-1.5}^{+2.0}$ and $73.17(72.74)^{+0.55}_{-0.77}$ km/s/Mpc for axion-like EDE and AdS-EDE, respectively. The axion-like EDE can fit the data significantly better ($\Delta \chi^2 \lesssim -10$) than $\Lambda$CDM, which is mainly driven by the ACT data. It is found again that if the current $H_0$ measured locally is correct, complete resolution of the Hubble tension seems to be pointing towards a scale invariant Harrison-Zeldovich spectrum of primordial scalar perturbation, i.e. $n_s=1$ for $H_0\sim 73$ km/s/Mpc.